1. Field of the Invention
The present invention relates to an image processing device capable of performing encoding processing according to a compression method for compressing multilevel image data and encoding processing according to a compression method for compressing binary image data, and to an image reading device equipped with the image processing device.
2. Description of the Related Art
There is a color digital copying machine furnished with a technique of automatically determining whether an image read by the image reading portion is a monochrome (black and white) image or a color image by the ACS (Auto Color Selection) processing (for example, JP-A-11-155045). Further, there is a copying machine furnished with a capability of enabling the user to select whether the encoding processing by the MMR (Modified Modified Read) (ITU-T T.6) compression method for compressing binary image data or the encoding processing by the JPEG (Joint Photographic Experts Group) compression method for compressing multilevel image data is to be performed when the image is determined as being a monochrome image from the result of the ACS processing in a case where the copying machine transmits the image data to an external device (for example, a personal computer, hereinafter abbreviated as PC), and this copying machine is now available in the market.
Meanwhile, when red and black are the colors of a two-color document, the document is not determined as being a two-color document by the ACS processing. This poses a problem that although the document is a two-color document, processing in the ACS mode is performed in the same manner as in the full-color mode. In order to solve this problem, JP-A-2007-97169 discloses a technique to determine whether a document is a full color document, a black document, or a two-color document on the basis of color information of the image data using histogram information and color difference level information, so that image processing is performed according to the determination result.
Incidentally, for the copying machine furnished with the capability of enabling the user to select the type of encoding processing in a case where the image is a monochrome image, there has been an increasing need to improve the convenience of the encoding processing type selecting capability.